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Synthesis and Catalytic Applications of Novel Zeolites and Mesoporous Materials
Increasing attention is being paid to zeolites as catalysts, which are expected to make a key contribution to the solution of the problems in resources, environment and energy. Zeolites are unique materials having intracrystalline pores of a molecular size, and zeolites whose structure are precisely controlled in sub-nano order can be selectively synthesized with the help of organic structure-directing agents. Through isomorphous substitution of metal atoms for the framework silicon atoms and incorporation of metal cations into the in-pore space, zeolites having high performance on applications in catalysis and adsorption can be obtained. | |
Prof. Takashi Tatsumi
Tokyo Institute of Technolog
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Dr. Takashi Tatsumi has carried out basic research on the synthesis of zeolites to be applied to petrochemical reactions and developed new methods for preparing catalysts having much improved functions. Shape-selective and regio-selective catalysis controlled by the pore structure of zeolites and microenvironment of the active center of catalysts has been also attained. These zeolites can be applied to a variety of chemical transformations without wastes and by-products, thus making them ecologically more acceptable and environmentally safer.
TS-1 is a titanosilicate zeolite where Ti is introduced into the framework of zeolites of the MFI structure. Titanosilicates demonstrate redox catalysis, quite distinct from conventional aluminosilicate zeolites. Dr. Tatsumi has discovered that TS-1 zeolite can catalyze the oxidation of chemically inactive simple alkanes at low temperature using H2O2 as oxidant. This discovery highlighted a special feature of TS-1 as a unique oxidation catalyst, attracting attention of a large number of researchers in the area of zeolites catalysis. He has succeeded in synthesizing new types of zeolites containing Ti in the framework such as Ti-SAPO-37, Ti-MWW, and Ti-YNU-1 and also Ti-containing mesoporous molecular sieves. He has also carried out the solid-state synthesis of Ti-beta, which could be an improved synthesis method. It is particularly noteworthy that Ti-MWW zeolite showed an alkene epoxidation activity several times as high as TS-1 that is a current industrial catalyst. Ti-YNU-1 has a new type of zeolite topology with 12-membered ring large pore; therefore it showed a very high activity in the epoxidation of bulky cyclic alkenes. It has been made clear that in this type of liquid phase oxidation using aqueous H2O2 as oxidant the hydrophobicity of the catalyst surface is critically important. Thus it has been revealed that the introduction of organic moieties resulted in the enhancement of the catalytic activity of Ti-containing mesoporous materials. Furthermore, he has synthesized a novel inorganic-organic hybrid zeolite ZOL, in which a methylene group is incorporated as a lattice. This hybrid zeolite material is synthesized from an organosilane with a bridging methylene group between two silicon atoms (Si-CH2-Si) to be substituted for a siloxane bridge (Si-O-Si) and has changed the concept of gzeolitesh that has been considered as silica-based porous crystalline materials. ZOL materials have high hydrophobicity and demonstrate the shape-selectivity in hydrocarbon adsorption. He has also succeeded in expanding interlayer pore of zeolites of a layered type by silylating layered precursors of zeolites followed by calcination. This is a new methodology of building a variety of zeolites structures, those with large pores in particular, starting from layered sheets of zeolites as nanoparts.
Mesoporous molecular sieves have attracted much attention of chemists and materials scientists because of emerging applications in catalysis, adsorption, sensors, and separations. They are analogous to zeolites, but their pore size is extremely large compared to zeolites pores, accommodating large reactants and products and mitigating the problem with their diffusion. Dr. Tatsumi has succeeded in the synthesis of a cubic 3-dimensional mesoporous molecular sieve Ti-MCM-48, which proved to be an active oxidation catalyst for bulky reactants impossible to be oxidized by zeolites. Although mesoporous molecular sieves had been reported to be unstable to water and mechanical impact, he has discovered that the mesostructure can be greatly stabilized by silylating the surface silanol groups on mesoporous materials. He has also found that in acidic synthesis using cationic surfactants as a structure directing agent (SDA) the mesostructures are transformed in the solid-solid manner and highly dependent of the counter anion as well as the cation, thus establishing the fundamental principles of control of the mesostructures. Although the use of anionic surfactants as a SDA for the synthesis of the mesoporous silica had been strongly desired, the synthesis of mesoporous silica by using an anionic surfactant had been unsuccessful for long time. He has developed a method of synthesizing the anionic surfactant templated mesoporous silica, AMS. The use of anionic surfactant as a SDA for the formation of the mesostructured silica-micelle composite has been presented as the gS- N+∼I- pathwayh that is promoted by the use of an organoalkoxysilane containing an amino group. Some of the AMS materials have mesostructures that have never been synthesized by using either cationic or nonionic surfactants; their structures have long-range periodical modulations. By using amino acid derived anionic surfactants, a new type of enantioenriched mesoporous material in the shape of helical rod, in which helical channels are running through. This is a purely inorganic chiral material, which could be utilized for the synthesis of and the separation of racemic mixtures into enantiomerically pure chemicals.
Dr. Tatsumi has also conducted researches into acid catalysis by zeolites; he found the effect of diluents in the Beckmann rearrangement, and achieved shape-selective control over alkene hydration. He has also discovered the unique features of metal nanoparticles and clusters incorporated into zeolite pores and led to the development of advanced catalysts active in alkane aromatization, selective synthesis of gasoline-range hydrocarbons from synthesis gas, and deep hydrodesulfurization of light oil.
In summary Dr. Takashi Tatsumi has achieved magnificent results through close coordination of the syntheses of novel porous materials with their application to useful catalytic reactions. He would deserve to receive the Chemical Society of Japan (CSJ) Award.
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